The invention relates to a method for sorting a gas-driven stream of generally flat and light-weight articles of varying dimensions through executing a, preferably optical, inspection and upon so finding a non-conforming article removing the latter from the stream. Such articles may result from production processes that are agriculture-based, or from other sources and a prime example for the products to be sorted are tobacco products such as leaves or parts cut therefrom or stems. Such products once packaged are transported, and then the products are handled for separating them again. Typical sizes for conforming particles of the product under consideration are without limitation lengths and widths in a range from 1 to 500 millimeters. Tobacco is relatively quite expensive and the separated products may be accompanied by various matters of non-conforming tobacco character, as well as by various categories of non-tobacco origin, such as the successive stages of the production may introduce. It is noted here that “optical” means “radiative” and thus including the use of radiation that is not visible for the eye. Moreover, inspection by means of other techniques like by acoustic waves might be feasible.
Prior art has realized the technical and economic usefulness of automatic sorting, but the present inventor has recognized that an optimized set-up would need at least some, but not necessarily all of the following features:                inspection with one or more relatively straightforward line-scan camera(s) arranged across the direction of motion of the articles;        orienting non-conforming articles in such manner that the detection device(s) will find the largest area of the article in question, whilst using only few or no moving parts for introducing and maintaining such orientation;        article motion and gas speed being adjustable and relatively uniform, in that relatively low speed will allow easy data processing, whereas higher speed will increase throughput, and requiring only few moving parts for attaining a low noise level;        a possibility for designing the apparatus through a substantially closed channel, also for keeping environmental dust level at low values; especially for a product like tobacco this is of great benefit;        removing the non-conforming matter through an underpressure facility that connects to the channel;        executing inspection and separation during substantially straight, in particular vertical, motion, inasmuch as such would tend to maintain particle orientation; a        free fall would be most advantageous, as such would tend to produce uniform particle speeds, especially in combination with gas-suction for particle removal;        and keeping the risk for jamming of the overall apparatus at an acceptably low value.        
Now in particular, U.S. Pat. No. 5,862,919 to Eason discloses the sorting of particles through feeding thereof by a horizontal conveyor belt, while separating both conforming and non-conforming articles through selectively activating a gas ejector during a falling trajectory of the particles, which trajectory will always deviate appreciably from a straight line. The present inventor has found that a straight line motion during both the inspection phase and the transmittal phase of the conforming articles is better for accurate detection and accurate removal of the particles. Furthermore, free motion of the particles allows for double-sided visual inspection. Moreover, such could be combined with better orienting the particles before inspection, which should give superior results.